Early stereophonic techniques featured directionality or "stereo imagery" by means of exaggerated signal manipulation. The "ping pong" transfers of virtual sources from side to side bear little resemblance to musical performances ranging from a solo performer to a full symphony orchestra, but instead serve to misdirect attention away from reality and toward "separation" as the hallmark of stereophonic sound. See, for example, U.S. Pat. Nos. 3,247,321, 3,184,550, 3,478,167, 3,171,891, and 3,280,258. This attention to separation has served to set unrealistic and unattainable goals in the quest for acceptable imitation of the original sound. Primary sounds are strongly affected by the acoustical characteristics of the immediate surroundings, whether they be a concert hall, a small studio, or even out-of-doors. The sense or hearing apparently involves a continuing spacetime analysis unconsciously performed by the ear/brain combination, and it is this analysis that provides the unmistakable credibility of real sound in a real location.
In the case of reproduced sound, the additional effect of acoustical characteristics of the region where the sound is reproduced combines irreversibly with the sound which might otherwise be heard at the original site, with the result that the final effect can be interpreted by the highly organized hearing mechanism as synthetic rather than natural.
The hearing sense relies strongly upon an "ambiance" created by a multitude of acoustic reflections and absorptions always present in any site where a sound occurs, and it is this feature which provides authenticity to what is heard. The nature of the ambiance, moreover, is transient due to reflections and absorptions which combine differently with direct sounds in a complex manner depending on the sonic radiation pattern of the source, its frequency, timbre, and location in any physically realizable surrounding. A spatially-distributed source such as an orchestra compounds this intrinsic complexity to an enormous degree. Restoration of an initial ambiance at the site of acoustic reproduction is the foundation of acoustic reality as interpreted by the hearing mechanism.